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7-7
Table 7-2 lists the maximum distances from the NAC terminal block to the last appliance
in a Class B configuration, depending on wire gauge and current. Use Table 7-2 to
calculate wire distances for your application if you are using Class B wiring.
Table 7-2. Class B Wiring Distances
Alarm
Current @
24 V
Max Distance
w/ 18 AWG
(0.8231 mm
2
)
Max Distance
w/ 16 AWG
(1.309 mm
2
)
Max Distance
w/ 14 AWG
(2.081 mm
2
)
Max Distance w/
12 AWG
(3.309 mm
2
)
DC
Resistance
0.25 A 840 ft. (256 m) 1,335 ft. (407 m) 2,126 ft. (648 m) 3,382 ft. (1,031 m) 12 Ohms
0.50 A 420 ft. (128 m) 667 ft. (203 m) 1,063 ft. (324 m) 1,691 ft. (515 m) 6 Ohms
0.75 A 280 ft. (85 m) 445 ft. (136 m) 709 ft. (216 m) 1,127 ft. (344 m) 4 Ohms
1 A 210 ft. (64 m) 334 ft. (102 m) 532 ft. (162 m) 845 ft. (258 m) 3 Ohms
1.25 A 168 ft. (51 m) 267 ft. (81 m) 425 ft. (130 m) 676 ft. (206 m) 2.4 Ohms
1.50 A 140 ft. (43 m) 222 ft. (68 m) 354 ft. (108 m) 564 ft. (172 m) 2 Ohms
1.75 A 120 ft. (37 m) 191 ft. (58 m) 304 ft. (93 m) 483 ft. (147 m) 1.71 Ohms
2 A 105 ft. (32 m) 167 ft. (51 m) 266 ft. (81 m) 423 ft. (129 m) 1.5 Ohms
2.25 A 93 ft. (28 m) 148 ft. (45 m) 236 ft. (72 m) 376 ft. (115 m) 1.33 Ohms
2.50 A 84 ft. (26 m) 133 ft. (41 m) 213 ft. (65 m) 338 ft. (103 m) 1.2 Ohms
2.75 A 76 ft. (23 m) 121 ft. (37 m) 193 ft. (59 m) 307 ft. (94 m) 1.09 Ohms
3 A 70 ft. (21 m) 111 ft. (34 m) 177 ft. (54 m) 282 ft. (86 m) 1 Ohm
Notes:
• Max Distance = distance from SPS or RPS to last appliance.
• This table is calculated at 49 degrees Centigrade (120 degrees
Fahrenheit). If you are installing in locations that could be exposed to
higher temperatures, refer to NEC Table 7 and 8 in NFPA code, or
applicable local standard.
• Distances are based on a 3 V drop, and take into account the worst-case
panel output voltage. These distances are worst case to allow for one
single load at the furthest point.
• If circuit integrity wire is used instead of housing cable in a fire rated
enclosure, reduce wiring distances by 38 feet (12 m) for every 10 feet (3
m) of potential exposure.
• For other wire gauges (e.g. 4 mm
2
) multiply the distance specified for the
nearest wire size by the ratio of the wire area, e.g. for 3A on 4 mm
2
look
up 3A on 12AWG (3.3 mm
2
) and multiply the resulting 86m x 4.0/3.3 =
104m.
Continued on next page
Power Supply Wiring Distances, Continued
Class B NAC
Wiring Table